At the beginning switch off the cell phone by pressing the Power button.Afterwards press and hold together: Volume Up + Home + Power button, until you see Samsung logo.Then select from Recovery Mode menu "wipe data / factory reset" using Volume buttons to navigate and Power button to confirm.Choose "Yes -- delete all user data" to confirm the whole operation.After that select option "reboot system now".Well done! The hard reset has just been performed.

OR

Start by turninng on the device.From the Home Screen go to Menu and then to Settings.Tap Backup & reset and then Reset device.To confirm your choice select Erase everything.That's all.